1. Field of the Invention
The present invention relates to Multi-view Video Coding (MVC), and more particularly to a method and an apparatus for obtaining predicted illumination compensation value and an illumination compensation flag value during the process of illumination compensation in multi-view video coding.
2. Description of the Related Art
With development in video technologies, analog picture processing methods are being replaced by digital picture processing methods. As a result, it has become possible to provide users with pictures which are clearer and have higher picture qualities than pictures captured with older technologies. The improvement in the picture quality has provided users with a much stronger feeling of presence. Recently, High Definition (HD) Television (TV) service for broadcasting a high quality picture is being provided and commercialization of a Digital Multimedia Broadcast (DMB) service transmitting vivid and clear pictures regardless of the place is being prepared. However, the high quality digital video service, which improves the quality of only the picture itself, has a limit in improving the degree of freedom and the feeling of presence that users' have. Representative elements degrading the feeling of presence in the use of a picture include a camera having a fixed view and a picture lacking depth. The fixed camera view degrades the degree of freedom, since it does not allow a user to view a prospective other than that of a current picture while the user views the current picture. Further, since a person can see an object by their eyes being oriented in the same direction from different positions, the person can feel the depth of the object by means of binocular disparity. However, the picture obtained by the fixed camera cannot give the feeling of depth, as it does not take binocular disparity into consideration. In order to solve this problem, a method of simultaneously obtaining multi-view pictures through multiple cameras at multiple viewpoints is being developed.
A scheme for coding multi-view pictures as described above is called a Multi-view Video Coding (MVC) scheme. The MVC refers to a scheme for processing sequences of multiple views of pictures obtained through multiple cameras. According to the MVC, multiple cameras are located at different distances from the same object and/or their orientations toward the same object. The multi-view pictures obtained through the multiple cameras show different degrees of reflections of light from the surface of the same object according to their directions, while the pictures of the views are highly related. This characteristic of the multi-view pictures results in differences in the brightness and color of the pictures for the same object according to the particular view. Therefore, in order to improve the encoding efficiency in the multi-view video coding, the above-described characteristic of the multi-view pictures should be taken into consideration.
The multi-view video coding, standardization of which is actively in progress, is searching for a method for improving an encoding efficiency in consideration of the two above-described characteristics of the multi-view pictures based on the H.264/MPEG-4 part 10 Advanced Video Coding(H.264/AVC), which is an existing international standard for video coding. For example, a hierarchical B-picture coding, which is a method for supporting a temporal scalability in a Joint Scalable Video Coding (JSVC) defined in the H.264/AVC, is also applied to an intra-view prediction coding within the multi-view video coding. Further, in the multi-view video coding performs, an inter-view prediction coding is also performed in parallel, so as to improve the coding efficiency.
FIG. 1 illustrates an example of a prediction structure showing intra-view prediction and inter-view prediction relations in the multi-view video coding. In the example shown in FIG. 1, eight views exist and the Group of Pictures (GOP) of the temporal direction has a size of 8. In FIG. 1, each of S0, S1, S2, S3 . . . S7 indicates one view, and T0, T1, T2, T3, . . . T100 indicate a temporal direction.
Referring to FIG. 1, it is noted that a prediction coding in the temporal direction is performed by using the hierarchical B-picture coding defined in the H.264/AVC in each view. Further, in each view, a picture of the first time band T0 and pictures (at T8, T16, T24, . . . ) spaced every 8 frames (which is the size of a GOP) away from the picture of the first time band T0 are called “anchor pictures.” For the anchor pictures, only the prediction (i.e. inter-view prediction) from neighbor views is performed. For example, at the time bands T0, T8, T16, T24, . . . , prediction is performed for the S2 view from the S0 view of the same time band, for the S1 view from the S0 view and the S2 view of the same time band, for the S4 view from the S2 view of the same time band, for the S3 view from the S2 view and the S4 view of the same time band, for the S6 view from the S4 view of the same time band, for the S5 view from the S4 view and the S6 view of the same time band, and for the S7 view from the S6 view of the same time band. In the case of the S7 view, since it is the last view, its prediction is performed from the S6 view.
For non-anchor pictures, prediction of the temporal direction is basically performed, and prediction from neighbor views is additionally performed for every second view (i.e. S1, S3, S5, and S7). That is, not only intra-view prediction of the temporal direction is performed, but also inter-view prediction is performed for the S1 view from the S0 view and the S2 view, for the S3 view from the S2 view and the S4 view, and for the S5 view from the S4 view and the S6 view, etc.
The multi-view video coding, international standardization of which is currently in progress, employs an illumination compensation method in order to improve a coding efficiency by compensating for a difference between luminance signals existing in the temporal direction or between views.
Illumination compensation-related data include flag information indicating if a current block uses illumination compensation, an illumination compensation value that includes an IC offset or a Difference Value of Illumination Change (DVIC; a luminance signal average difference between a current block and a reference block), and information regarding if illumination compensation will be performed and regarding a predicted illumination compensation value derived from neighbor blocks.